There are many uses for pumps and hydraulic motors which are capable of variable flow and pressure operation. These types of devices are widely used in industrial, commerical and consumer applications where, in a typical application, a fixed speed electric motor drives a pump and fluid discharged from the pump drives a hydraulic motor at some other location. Variable speed or load demands at the hydraulic motor are accommodated by various means. In some instances a variable speed drive such as a variable voltage D.C. motor or a variable frequency A.C. drive motor or a fixed speed motor with a belt type variable pulley drive or an internal combustion engine are used to vary the speed of the pump. When the pump speed is varied the volume of fluid transmitted to the hydraulic motor is varied to accommodate the load conditions. In addition to these methods, other methods such as bypassing part of the output of the pump, especially if the pump is coupled directly to fixed speed drive motor, are frequently used.
All of these methods of providing for variable loads in pump/hydraulic motor drive systems require either a variable speed primary driver or an efficient means of achieving fluid bypassing. In addition, where a variable speed primary driver is used especially in the case of internal combustion engines, such as in automotive use, where the engine is coupled to an automatic transmission, the primary driver is rarely operated at or near the point of optimum efficiency due to the speed and load variations encountered.
An efficient, reliable and relatively simple variable displacement pump/hydraulic motor could be used to advantage in any of the instances cited above. More economical fixed speed primary drivers could be used with such a device to efficiently accommodate normal load variations. In addition, such a device would permit internal combustion engine driven systems to operate at peak engine efficiency for nearly all speeds and load conditions.
The enhanced efficiency available when engine operation can be separated from speed requirements can be achieved with a variable displacement pump/hydraulic motor if it is capable of permitting a wide but continuous range of fluid pumping rates over a broad range of fluid pressure to achieve the equivalent of a continuously variable transmission. A range of ratios of 12 to 1 is suggested by the literature. (A Continuously Variable Transmission for Automotive Fuel Economy by J. H. Kraus, C. E. Kraus and M. E. Gres, Excelermatic, Inc. S.A.E. 751180. 3307 to 3316).
There have been a number of prior inventions in the field of variable displacement sliding vane pumps/hydraulic motors. These prior inventions have certain limitations which somewhat limit their utility. A typical example of the limitations present in the prior art can be found in U.S. Pat. No. 4,046,493, Sliding Vane Machine invented by Torsten Olund. This invention described a machine in which the vanes(5) in the pump must be compressed abruptly into their grooves(4) during rotation of the rotor(3) to bypass partition walls(6) separating pressure chambers within the pump housing.
Other variable displacement sliding vane pumps/hydraulic motors such as the one illustrated in S.A.E. paper 790725 entitled "A New Automatic Transmission for Improved Fuel Economy--General Motors THM 125" presented by Erkki A. Koivunen and Philip A. Lebar, Jr., Hydramatic Division of General Motors Corporation, June, 1979, incorporates an eccentric rotor and vane assembly contained in a slide housing which is mounted on a pivot to enable the eccentricity of the rotor assembly and therefore the pumping capacity to be varied. This pump, however, is used only to replace the conventional pump in the transmission and the usual clutch/gear sets are used to achieve the necessary gear reductions.
The present invention, a variable displacement sliding vane pump/hydraulic motor, can be used both as a pump and as a hydraulic motor. It incorporates the capability of virtually unlimited variability from zero flow to maximum pumping capacity. This capability is achieved without the use of internal partitions.